Re: [Xen-devel] Outreachy bite-sized tasks

[Paulina Szubarczyk <paulinaszubarczyk@xxxxxxxxx>]

On Fri, 2016-04-01 at 15:35 +0200, Roger Pau Monné wrote:
> Please don't top post, it breaks the flow of the conversation.
> 
> I'm also adding Anthony (one of the QEMU/Xen maintainers).
> On Fri, 1 Apr 2016, Paulina Szubarczyk wrote:
> 
> > Hi Roger,
> > 
> > An another point that needs to be filled up in the application is timeline.
> > I made the proposition of it, I am not sure if it should be more complex. 
> > Could you look at it in your free time?
> > 
> > Timeline:
> > 
> > 22 April - 22 May [Before the intership]
> >  * Elaborate performance measurement methodology. That may include putting 
> > trace
> >     points using TRDCS and performing read operation with varying block 
> > sizes on 
> >     different storage devices as in [3].
> 
> Could you elaborate on TRDCS? I've tried googling for it, but nothing came 
> up.
I mistyped TRDCS, I meant putting trace points in the application to
measure the time spent in each place as shown in the talk[3]. But is I
did more research concerning the measurement I think that the good idea
would be using fio and make similar test as Adriana did during her
OWP[4] when she worked on implementing multi-queue support for
xen_backend in Linux.  

> Also, I think it would be good to write down which tool are you going to 
> use in order to perform those measurements, and how/which block sizes are 
> you going to test. Also keep into account that apart from block sizes you 
> also have to take into account the number of parallel workers and the 
> queue depth of each one.
> 
> Regarding the different storage devices, we usually did benchmarks using a 
> ramdisk, but Linux intorduced a null-block device [0] not long ago that I 
> think could be used to model different storage devices without actually 
> having to buy them.
I make myself familiar with the protocol and I debug the qdisk during
attaching one of ram devices to follow how it works. I also wondered if
maybe I could make a change to 'xl create' such as when it is run in the
qemu debug mode doesn't terminate when Device Mode isn't ready yet,
because sometimes is hard to catch the moment when the connection to
gdbserver is possible.

Whereas I saw the implementation of indirect descriptors and the
multi-queue support by creating multiple rings, I couldn't find the
information of grant copy. Do you mean by that hypervisor-driven copy of
grant pages between domains instead of mapping them? 
> 
> I don't expect that you do all this now, but it is important to think 
> about the different scenarios/benchmarks and plan ahead, so that you 
> don't end up running benchmarks that are not useful.
> 
> >  * Gain a profound knowledge about implementation of xen-blkback in Qemu 
> > and Linux kernel.
> > 
> > 23 May - 6 June [Begin of the intership - up to two weeks]
> >  * Prepare and improve performance measurement test.
> >  * Gather and document the results.
> > 
> > 6 June - 23 August
> >  * Base on the analysis and the task description implement performance 
> > improvement future 
> >    inside of QEMU's xen-blkback.
> >  * Prepare and run regression tests and continue performance measurement 
> > for 
> >    each implemented feature.
> >  * Document the results.
> > 
> > 15 August - 23 August [Close to the end]
> >  * Sum up the work:
> >    - indicate the obstacles
> >    - form the conclusion and
> >    - indicate future work.
> > 
> > References:
> > [1] http://lxr.free-electrons.com/source/drivers/block/xen-blkback/blkback.c
> > [2] 
> > http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/include/public/io/blkif.h
> > [3] 
> > https://events.linuxfoundation.org/sites/events/files/slides/20131025%20-%20Storage%20Performance%20PDF.pdf
> 
> [0] https://www.kernel.org/doc/Documentation/block/null_blk.txt
[4] https://github.com/ariava/xen-blk-mq-benchmark

Paulina


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